Known heat-resistant agents for organopolysiloxanes include organopolysiloxanes having hindered phenol residues (Japanese Patent Announcement 47-3922 (1972) and Japanese Patent Announcement 7-42472 (1995) and organopolysiloxanes having phenol residues (Japanese Patent Application Early Disclosure No. 7-216376 (1995)).
However, organopolysiloxanes having hindered phenol residues have large organic group components, for which reason they exhibit good solubility in organopolysiloxanes having, for example, long chain alkyl groups, aryl groups and aralkyl groups, and can confer heat resistance on these organopolysiloxanes. However, they lack solubility, for example, in dimethyl polysiloxane, dimethyl siloxane-methylphenylsiloxane copolymer and dimethylsiloxane-methyl(3,3,3-trifluoropropyl siloxane copolymer, all of which comprise dimethylsiloxane units. These diorganopolysiloxanes are turbid and sufficient heat-resistance cannot be conferred on these diorganopolysiloxanes. Likewise, organopolysiloxanes having phenol residues cannot confer sufficient heat resistance on organopolysiloxanes.